Have Gecko-specific requirements file for wptrunner

Installing non-vendored dependencies for wptrunner in CI presents a
problem. Gecko CI can only access packages that we have explicitly
mirrored into our internal systems. Generally we try to avoid such
dependencies, but in the case of packages with a binary component
vendoring isn't possible.

Previoulsy we just depended on the webtransport requirements file from
upstream, but this was out of sync and pinned to an older version. Now
that we also require Pillow to be installed, move to a system where
there's a specific file in the Gecko source tree that we depend
on. The wptsync could be taught to help keep this up to
date (e.g. filing a bug when upstream updates one of the referenced packages).

Differential Revision: https://phabricator.services.mozilla.com/D258691

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1979290
gecko-commit: 84f8270cbd2f1a3e95ce956bbba08a320ce90371
gecko-reviewers: Sasha

Author: jgraham

tools/wptrunner/requirements.txt

@@ -9,4 +9,4 @@ pillow==11.3.0; python_version >= '3.9'
 requests==2.32.3
 types-requests==2.32.0.20241016
 urllib3==2.2.2
-aioquic==0.9.21
+aioquic==1.2.0